February 2011 - Report and Summary

by Robert K. Peters, Ph.D. - National Weather Service Cooperating Observer

The month of February 2011 was cooler and drier than normal. The first half of the month was very cold, while temperatures climbed well above normal during the last half of the month.

As had been the case since early-December, two upper air flow patterns combined to produce the cold weather: a northwest-to-southeast orientation of the Pacific-North American Tele- Connection, and a northeast-to-southwest orientation of the Arctic Oscillation.

In early February, these two patterns reversed, and the flow of Arctic air from Canada stopped.

The month, however, was 7.7 deg. Warmer than the also cold February 2010, and 1.43 inches drier. Year-to-date rainfall was 0.71 inch greater in 2011 than in 2010. The thirty-day outlook had called for above normal temperatures and below normal precipitation.

The month began with a strong outbreak of Arctic air, which moved into the region on the morning of the 1st and persisted into the morning of the 5th.

A line of thunderstorms accompanied the Arctic cold front, some of which approached severe limits, and resulted in rainfall of between one-half and one inch. A small tornado touched down in eastern Rusk County.

Strong winds through the 2nd brought very low wind chill equivalent temperatures, and resulted in rolling power black-outs.

An upper air disturbance crossed on the morning of the 4th. This produced snow of between two and eight inches. Tyler received 4.0 inches, with the 8.0-inch measurement at Yantis. The temperature was below freezing in Tyler for 97 consecutive hours the string commencing at 9 a.m. on the 1st and finally ending at 10 a.m. on the 5th.

Temperatures warmed through the 7th, when another Arctic front arrived. A second, and much stronger Arctic front, arrived on the 9th. This was accompanied by light freezing rain and snow with no accumulation. The cold persisted into the 11th, when a warming trend commenced.

This warming trend, with surface and upper air high pressure in control, sent temperatures to between 8 and 15 degrees above normal from the 14th through the 20th. There was no rain during the period.

Weak cold fronts crossed on the 21st, 25th, and 28th. The latter two were accompanied by showers and thunderstorms. Even with these cold outbreaks, temperatures during the latter half of the month ran well above normal, though there was a slight lowering of the above-normal values after the 21st.

KEY TO SYMBOLS:

A = HAIL

B = BLOWING

D = DUST

F = FOG

H = HAZE

IP = SLEET

K = SMOKE

L = DRIZZLE

R = RAIN

S = SNOW

T = THUNDERSTORM

Z = GREENWICH MEAN TIME

ZL = FREEZING DRIZZLE

ZR = FREEZING RAIN

- = LIGHT

+ = HEAVY

The reporting period for temperatures and phenomenon on each day is for the twenty-four hours ending at midnight hours GMT--6 p.m. CST and 7 p.m. CDT. The reporting period for precipitation is for the twenty-four hours ending at noon GMT--6 a.m. CST and 7 a.m. CDT. All times are given using the twenty-four hour clock, and are expressed in Greenwich Mean Time.

Observations are from NWS Station 41/9207/4 in Tyler, Texas. The term "normal" refers to averages from the standard climatic period 1971-2000.